Heat and drought stress responses alter grain characteristics by impeding starch precursors of wheat

In semi-tropical regions, particularly in Punjab (India), drought and high temperature stress are serious constraints for wheat production. Understanding the key metabolic steps may help the breeders and biotechnologist to develop heat and drought tolerant genotypes. Six wheat cultivars, namely PBW 343, PBW 550, PBW 621, PBW 175, C 306 and HD 2967 were extensively characterized for transformation of sugars to starch under heat and drought stress conditions. Significant reduction in enzyme activities of ADP-Glucose pyrophosphorylase (AGPase), alkaline inorganic pyrophosphatase and phosphofructokinase (PFK) in conjunction with reduced starch content under heat and drought stress conditions was apparent. However, contents of reducing sugars and fructans were increased while amylose and amylopectin content decreased. Correlation analysis revealed positive correlation of amylose with alkaline inorganic pyrophosphatase and starch with AGPase and PFK. Role of PFK was evident from correlation between AGPase and PFK indicating its predominant role in providing substrate for AGPase activity. Significant effects of stress treatments (T), genotype (G) and genotype-by-treatment (G×T) interaction were observed for AGPase, alkaline inorganic pyrophosphatase and PFK, amylose, amylopectin, starch, total sugars, fructans, 1000 grain weight and plant height. Thousand grain weights decreased more under heat stress as compared to drought stress indicating higher severity of the former stress.

Modulation of proline metabolism under drought and salt stress conditions in wheat seedlings

Drought and salinity are the major environmental constraints that limit plant growth and productivity. In the present investigation, shoots of seven day old plantlets of nineteen wheat genotypes (PBW621, PBW660, PBW175, HD3086, WH1105, HD2967, C306, C273, C518, C591, Type 11, Excalibar, Gladius, Drysdale, Babax, Krichauff, Kharchia, Krl 1-4 and Krl 19) were evaluated for proline metabolism and its cross-talk with various biochemical parameters under water deficit, water withholding and salinity stress conditions. Principle component analysis categorized the genotypes into four groups: i.e. drought tolerant (Excalibar, Krichauff, Babax, Drysdale, Gladius and C306), salt tolerant (Kharchia, Type11, Krl1-4 and Krl19), low stress tolerant (C273, C518 and C591) and susceptible (HD2967, PBW621, WH1105, HD3086, PBW660 and PBW175). Tolerant genotypes possessed increased proline content and 1,1 diphenyl-picryl hydrazyl (DPPH) radical scavenging activity along with the reduced magnitude of thiobarbituric acid reactive species in parallel with decreased H2O2 content. Proline accumulation in shoots of tolerant genotypes under stress conditions may be an adaptative strategy, as it supplies energy for growth and lowers the generation of free radicals and reduces the lipid peroxidation linked membrane damage resulting in their stabilization. Glutamate dehydrogenase might have played a dominant role in ammonium assimilation and glutamate biosynthesis, leading to an increased glutamate pool, which via pyrroline-5-carboxylate synthetase activity led to enhanced proline accumulation in tolerant genotypes under stress conditions. Water withholding condition induced the stimulation of proline synthesis via increased glutamate dehydrogenase (GDH), pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR) activities with inhibition of oxidation via reduced proline dehydrogenase activity to a large extent as compared to water deficit and salt stress conditions. Our results highlight that in certain genotypes, GDH under water deficit, P5CS and PDH under salt stress and P5CR under water withholding stress condition were responsible for stress tolerance and could be used as a selectable marker.

Purification and characterization of neutral invertase from chickpea nodules.

Neutral invertase from nodules of chickpea (Cicer arietinum L.) was isolated and purified by ammonium sulphate fractionation, gel filtration and DEAE-cellulose column chromatography. The purified enzyme was stable between 0 to 40 degrees C beyond which it was irreversibly denatured. Optimum temperature and pH of the enzyme were 37 degrees C and 7.0, respectively. K(m) for sucrose was 14.2 mM and Vmax was 4.8 mumole hr-1. The enzyme was inhibited by several metal ions. From the temperature effect on K(m) and Vmax values, the energy of activation (Ea), enthalpy change (delta H) and entropy change (delta S) of the enzyme were calculated to be 147 kJmol-1, -4.10 kJmol-1 and -2.33 JK-1mol-1, respectively. By employing photo-oxidation and chemical modification and by studying the effect of pH on K(m) and Vmax, the involvement of sulphydryl-, imidazole- and alpha-amino groups in the active site of the enzyme has been indicated.